1. Field of the Invention
The present invention relates to seals between an outer cylindrical frame and an inner cylindrical frame and particularly to seals which permit rotational movement in a dial indicator of a gauge or other similar instrument.
2. Description of Prior Art
In conventional dial indicators for gauges and the like, a cylindrical outer frame is rotatably fitted to the outside of a cylindrical inner frame. A dial plate or face is rotatably supported on its circumference for movement with the cylindrical outer frame such that the pointer of the dial indicator can be set to zero by rotatable movement of the cylindrical outer frame and dial plate or face. In this type of dial indicator, water, oil, or other liquid or gaseous contaminant is liable to get into the inner cylinder through a gap between the outer cylindrical frame and the inner cylindrical frame when the instrument is in use. As a consequence of this, the magnifying gear system within the inner frame may become rusted, or the surface of the dial plate may become stained with oil, or another similar event may occur rendering the instrument unreliable or non-functioning.
To eliminate this drawback, it has been conventional practice to provide a circumferential, rectangular channel or groove on the inner frame. A sealing ring was provided in the annular groove, the sealing ring abutting the flat, inner surface of the outer frame. In this configuration, the sealing ring elasically presses on the inside of the outer frame and the annular groove of the inner frame in a manner well known with the conventional practice of the use of so-called O-rings.
When initially constructed in this fashion, a reliable seal was established between the inner and outer frame which prevented the unwanted invasion of liquids or vapors which might damage the dial indicator. When, however, the sealing ring is worn by the repeated rotation of the outer frame due to zero-setting, the sealing ring will fail to be uniformly pressed against the entire circumference of the outer frame. As a result, a gap between the sealing ring and the outer frame can occur which will permit the invasion of a contaminant into the dial indicator. It is, therefore, the primary object of the present invention to provide an improvement in the combination of a cylindrical outer frame coaxially rotatably mounted on the outside of a cylindrical inner frame which will maintain a sealed condition therebetween.